Conventionally, internal combustion engines of one type in which fuel is injected into the inside of a combustion chamber, that is, internal combustion engines of the in-cylinder injection type, for example, have the distal end portion of a fuel injection valve inserted into and supported by an insertion hole of a cylinder head and have the proximal end portion of the fuel injection valve inserted into and supported by a delivery pipe (a fuel injection valve cup), whereby the fuel injection valve is provided across the cylinder head and the delivery pipe. Usually, when the fuel pressure supplied through the delivery pipe changes due to injection or stopping of the fuel, vibration based on the change in fuel pressure occurs to the above fuel injection valve. For this reason, it is often the case that a vibration insulator to absorb and damp such vibration of a fuel injection valve is attached between the fuel injection valve and an insertion hole of a cylinder head.
On the other hand, the cylinder head and the delivery pipe are originally parts of separate bodies. Therefore, changes in the relative positions thereof, which are caused by, for example, tolerances associated with production or processing of these parts, tolerances associated with assembly in the production, thermal deformation, and various vibrations that accompany the operation of the internal combustion engine, are unavoidable. That is, the axis of the fuel injection valve provided across the cylinder head and the delivery pipe becomes inclined relative to the axis of the insertion hole of the cylinder head, whereby positions at which the fuel injection valve is supported by the cylinder head and the delivery pipe deviate from correct positions. Further, such positional deviation causes problems such as partial slack of an O-ring at the proximal end of the fuel injection valve, the O-ring serving to prevent fuel leakage between the fuel injection valve and the delivery pipe (fuel injection valve cup). Therefore, the positional deviation may possibly cause fuel leakage.
For this reason, insulators designed to not only absorb and damp vibration of the fuel injection valve but also reduce the influence of such inclination of the axis of the fuel injection valve have been proposed, and an insulator described in Patent Document 1 is known as one example thereof. The insulator described in Patent Document 1 includes an annular adjustment element sandwiched between a shoulder section having an opening into a side wall of an insertion hole (a receiving hole) of the cylinder head and a stepped section of a fuel injection valve arranged by being inserted into the insertion hole, the diameter of which is enlarged in a tapered manner to face the shoulder section. The adjustment element has a first leg extending along the shoulder section of the insertion hole and a second leg extending along the tapered stepped section of the fuel injection valve. A structure elastically supporting the fuel injection valve with respect to the cylinder head is obtained by having the first leg in surface contact with the shoulder section of the insertion hole and having the second leg in surface contact with the tapered stepped section of the fuel injection valve.